Monday, June 12, 2017

The axillary nerve and adhesive capsulitis


The axillary nerve (yellow arrow) and the posterior humeral circumflex artery (red arrow) in the region of the quadrilateral space. Note proximity to the inferior capsule.

The axillary nerve is closely related to the inferior capsule of the shoulder. It passes inferior to the subscapularis muscle and travels adjacent to the capsule before entering the quadrilateral space.

The axillary nerve is associated with adhesive capsulitis in at least 2 ways.

First, the axillary nerve can be irritated in the setting of inflammation and thickening of the inferior capsule. The evidence for this is somewhat anecdotal, but makes anatomic sense. The image below is from a patient with adhesive capsulitis. Note the teres minor atrophy (green arrow) in the setting of thickening of the inferior capsule (blue arrow), and constrained fluid in the joint (orange arrow) being forced into the superior subscapularis recess (orange*). The bone lesions are from myeloma, in case you were wondering.



Second, the close proximity of the nerve to the joint capsule predisposes it to injury during arthroscopic capsule release for treatment of adhesive capsulitis. Risk of injury is decreased by placing the incision of the glenohumeral joint capsule at the glenoid insertion with the arm in the abducted and externally rotated position.

References

  • Jerosch J, Filler TJ, Peuker ET. Which joint position puts the axillary nerve at lowest risk when performing arthroscopic capsular release in patients with adhesive capsulitis of the shoulder? Knee Surg Sports Traumatol Arthrosc. 2002 Mar;10(2):126-9.
  • E. B. G. D. Santos, P. M. E. Souza (pdf). Teres minor beyond quadrilateral space syndrome: a pictorial review. ECR 2014 conference.

Tuesday, June 6, 2017

Sacrum

I was reading an article on the role of religion in the secular Turkish state and came across this statement:
It is possible -- such is the argument of Carter Findley in his Turks in World History -- that in doing so it drew on a long Turkish cultural tradition, born in Central Asia and predating conversion to Islam, that figured a sacralisation of the state, which has vested its modern signifier, devlet, with an aura of unusual potency.

You may be wondering what the heck a congenital variant of spinal segmentation has to do with religion. From the always-excellent Online Etymology Dictionary:

Bone at the base of the spine, 1753, from Late Latin os sacrum "sacred bone," from Latin os "bone" + sacrum, neuter of sacer "sacred" (see sacred). Said to be so called because the bone was the part of animals that was offered in sacrifices. Translation of Greek hieron osteon. Greek hieros also can mean "strong," and some sources suggest the Latin is a mistranslation of Galen, who was calling it "the strong bone."

Monday, May 29, 2017

Rind-like Perirenal Soft-Tissue Masses


Rind-like perirenal soft tissue masses: Retroperitoneal fibrosis Differential diagnosis for rind-like perirenal soft-tissue masses:
  • Lymphoma
    • Usually due to contiguous spread from retroperitoneal or renal lymphoma: Distinct imaging patterns: multiple masses, solitary mass, diffuse infiltrating mass, rindlike soft-tissue thickening, and direct invasion from adjacent retroperitoneal lymphadenopathy
    • Isolated perirenal lymphoma very unusual (<10% of cases): Uniformly attenuating rindlike soft-tissue mass.
    • Does not necessarily affect renal function.
  • Erdheim-Chester disease
    • Rindlike soft-tissue lesions surrounding the kidneys and ureters
    • Severe compression of renal parenchyma and ureters leads to progressive renal failure
    • Percutaneous nephrostomy made difficult because due to fibrous perinephritis.
  • Retroperitoneal Fibrosis (shown above)
    • Typically localized to infrarenal aorta and common iliac arteries
    • Isolated or related to multifocal fibrosclerosis (may include autoimmune pancreatitis, sclerosing cholangitis, scleroderma, Riedel thyroiditis, fibrotic pseudotumor of the orbit, and fibrosis involving multiple organ systems).
    • Perirenal involvement can be from extension from retroperitoneal fibrosis, without associated retroperitoneal fibrosis, or one of manifestations of multifocal fibrosclerosis
    • Perirenal involvement: Soft-tissue mass enveloping kidneys without displacing them.

References

Surabhi VR, Menias C, Prasad SR, Patel AH, Nagar A, Dalrymple NC. Neoplastic and non-neoplastic proliferative disorders of the perirenal space: cross-sectional imaging findings. Radiographics. 2008 Jul-Aug;28(4):1005-17.

Saturday, May 13, 2017

Toxic Osteoblastoma

Toxic osteoblastoma is an extremely rare variant of osteoblastoma that is associated with systemic symptoms, such as fever, anorexia, weight loss. There is also marked systemic periostitis, not only of the involved bone, but also at other skeletal sites.

Patients tend to be young children (5-7 years of age). On physical examination, there is massive swelling, warmth, and induration of the overlying skin and prominent superficial vessels overlying the lesion. Patients can also have hyperdynamic circulation and even high-output cardiac failure. Regional adenopathy can also be present.

The systemic response is thought to be due to an exaggerated immune response to the tumor. Interleukins can lead to fever and the diffuse periostitis, as well as anemia and massive limb swelling and vascular proliferation. Another possibility is toxic substances released by the tumor itself.

The lesions are highly vascular, and arteriovenous shunting within the lesion can lead to finger clubbing and diffuse periostitis and can account for hyperdynamic circulation.

Differential considerations include osteomyelitis and osteosarcoma.

References

Sunday, April 23, 2017

Nerve Root(s)


In season 3, episode 18 of Star Trek: Deep Space Nine Dr. Bashir has to deal with some deep-seated personal issues. One of these is the fact that he graduated second in his medical school class because he mistook a "pre-ganglionic fiber for a post-ganglionic nerve." Spoiler alert: He did it on purpose because he didn't want to deal with the pressure of being first.

Dr. Bashir is not alone. I see this lead to 2 errors every day in our trainees. The clinical implication is zero, because the referring physicians also don't make this distinction (two wrongs do make a right, apparently).

First, take a look at the image below:



Note that there are 2 nerve roots (dorsal and ventral) on each side (left and right). When you say a lumbar disc compresses a nerve root in the central spinal canal, you need to add an "s," because these dorsal and ventral nerve roots travels down together in the cauda equina. Next time you look at an axial T2-WI of the lumbar spine, see if you can see two distinct nerve roots on either side.

Second, note that once we're post-ganglionic, we're dealing with a nerve, not a root. So, if you're talking about a nerve root outside the foramen, you're about as anatomically correct as a Ken doll.


The same goes for the "nerve roots" of the brachial plexus and the famous Randy Travis Drinks Cold Beer mnemonic for the brachial plexus anatomy (sorry, Randy). All is not lost. Just replace Randy Travis with Nikola Tesla.

Reference

  • Basic anatomy that everyone ignores.

Sunday, April 16, 2017

Ventriculus Terminalis


The ventriculus terminalis (also known as the terminal ventricle and the fifth ventricle) is a rarely identified cerebrospinal fluid cavity within the conus medullaris. The ventriculus terminalis does not communicate with the subarachnoid space or the central canal of the spinal cord, and may actually be an embryonal remnant of the primitive central canal, leading some to refer to it a sinus terminalis instead.

They are occasionally associated with caudal regression of the spinal cord, Chiari type I malformation, lipomyelomeningoceles, and lumbosacral "lipomas." Some authors believe that all of us have some sort of cystic CSF space at the conus medullaris, but that it's simply larger [and detectable on imaging] in some people and tends to regress (but not completely resolve) over time.

The characteristic imaging features are more commonly seen in children: Cystic lesion of the conus medullaris without spinal cord signal abnormality. In adults, ventriculus terminalis is more likely to have septations and be associated with spinal cord edema, kyphotic deformity and spinal arteriovenous malformations.

Rarely, ventriculus terminalis can enlarge in the presence of meningeal hemorrhage or deformities of the vertebral canal. An enlarged or symptomatic ventriculus terminalis can be treated by cyst fenestration with or without shunting to the subarachnoid space, pleural cavity, or peritoneal cavity.

References

Monday, April 10, 2017

False Perpetuations: Main Portal Vein Size and Portal Hypertension

Perpetuation: A main portal vein (MPV) diameter >13 mm is "consistent with portal hypertension" (pHTN)

This cutoff of 13 mm is based on weak literature (mainly from the 1980's), some of which did not include comparison values of normal patients

  • One comparative study using ultrasound found (Radiology 1982; 142: 167-172):
    • In 79 patients with pHTN
      • 36 had a MPV diameter of <13 mm 
      • 33 had a MPV diameter >/= 13 mm
      • The MPV was not visualized in 10 patients
    • In the 45 control patients
      • The MPV diameter was < 13 mm in 41 cases
      • The MPV was not visualized in 4 patients. 

More recent studies have found that there is no significant difference in MPV diameters when comparing patients without cirrhosis to patients with cirrhosis, and the normal MPV diameter is significantly larger than the 13 mm cutoff

  • A study (Eur J Gastroenterol Hepatol 2004; 16:147-155) from King's College using ultrasound (49 controls and 14 cirrhotics) found: 
    • the average MPV diameters were 9.6 cm and 10.8 cm in patients without and with cirrhosis, respectively.
  • A second study (JCAT 2008; 32: 198-203) from UCSF using CT (59 controls and 67 cirrhotics) found:
    • The average MPV diameters were 14.5 cm and 14.8 cm in patients without and with cirrhosis, respectively.
  • Using CT, the MPVs in healthy renal donor patients were measured before and after the administration of intravenous contrast, and in the axial and coronal planes (Abdom Radiol 2016; 41:1931-1936). This study found:
    • The average MPV diameter was 15.5 +/- 1.9 mm
      • This value was significantly different than 13 mm
    • Post-contrast MPVs were 0.56 mm larger compared to non-contrast
    • A positive correlation between BMI and height versus MPV diameter
In fact, the MPV size can be reduced in portal hypertension and has been described as a sign of hepatofugal MPV flow (AJR 2003; 181: 1629-1633). This study found:
  • A MPV diameter of less than 1 cm is a highly sensitive (but not very specific) for MPV flow reversal in patients with cirrhosis